In the manufacture of small catheters, sometimes two or more lumens are needed that extend within the catheter. This has been previously accomplished by extrusion of the catheter about a plurality of metal mandrels, which then must be removed after the extrusion process to open the lumens. Typically, the metal mandrels are made of a copper alloy which can be stretched to facilitate their removal. However, the mandrel is then typically no longer useful, so that it must be recycled by melting and reextruded as a new mandrel.
Thus, there is a perceived need to reduce the number of expensive metallic mandrels which are used in the extrusion of catheters and the like.
Additionally, air mandrels have been used, in which the lumen of an extruded tube is maintained after its formation by means of a gentle air pressure. However, it has proven most difficult to manufacture multiple lumen catheters or the like with the use of air mandrels.
By this invention, a combined extrusion process is provided which exhibits advantages found in both air mandrel extrusion and wire mandrel extrusion. Specifically, a good bond can be obtained between various layers of catheters extruded by this invention. Also, great versatility is provided in the specific shape of at least one of the lumens provided in the extrusion process of this invention. For example, a lumen of crescent-shaped cross-section can be provided without the need for the use of a correspondingly-shaped wire mandrel which, of course, would add to the expense of the catheter. Nevertheless, advantages of good layer bonding and the like which are characteristic of wire mandrel catheter extrusion processes can be achieved in this invention.